1. Field of the Invention
The present invention relates to a superconducting oxide ceramic material and a method for manufacturing such a superconducting oxide material.
2. Description of the Related Art
Recently, superconducting ceramic materials have been attracting a great deal of attention. These materials were first reported by IBM's Zurich Laboratories in the form of Ba-La-Cu-O (BALACUO) type high temperature superconducting oxide material. In addition, the YBCO (YBa.sub.2 CuO.sub.6-8) types are also known. However, these types could be prepared only by mixing and firing various types of oxide powders to form tablets, so that even when a Tc onset of 90K was obtained, a sufficiently thin film was not possible. In addition, it was completely unknown that the surface portion on which the thin film is formed has non-superconductive characteristics and the same crystalline structure as the thin film.
The critical current density of these superconducting materials with polycrystalline oxide structure is small. In order to correct this problem, it is desired that all the ab surfaces of the crystal grains (also referred to as the C surface, the surface perpendicular to the C axis direction) be mutually oriented. In addition, because the difference between the coefficients of thermal expansion of the superconducting material and the substrate is large, when the superconducting material is made at temperatures higher than 650.degree. C., especially in the high temperature range of 900.degree. to 950.degree. C., there is the drawback that cooling at the temperature of liquid nitrogen induces cracking and the electrical conductance is inhibited. For this reason, it has been strongly required to carry out film formation at a temperature of 500.degree. C. or lower, so that there be a degree of freedom in the selection of the type of substrate. Furthermore, it is strongly desired that the Tco (temperature at which resistance is zero) of the superconducting oxide material be higher. It is desirable that activation be possible at the temperature of liquid nitrogen (77 K) or a higher temperature, and that, in turn, the Tco temperature of 90K or higher be available in the structure of the thin film.
With such an objective in mind, the inventor of the present invention filed Japanese Patent Application 62-75205 on Mar. 27, 1987 covering a "Method for manufacturing a superconducting material" which was a method for manufacturing a superconducting material by applying a magnetic field during a heating process.
The present invention is a further develpment of the above-mentioned invention.